Genome-wide maps of rH2A.X in wildtype and DNMT3b-KO HCT116 lines

Dysfunction of DNA methyltransferase 3b (DNMT3b) causes centromere instability but the underlying mechanism is unclear. We found that enforced expression of RNase H1 that removes R-loops, nucleic structures comprising an DNA-RNA hybrid, was sufficient to abolish DNA double-strand breaks (DSBs) at (peri-)centromeric sites in immunodeficiency-centromeric instability-facial anomalies (ICF) patient cells carrying DNMT3b mutation. However, ICF cells had lower steady-state level of centromeric R-loops than normal cells. Simultaneous knockdown of two DNA endonucleases, XPG and XPF, restored centromeric R-loops in ICF cells while reducing DSBs and chromosome segregation error. This suggests that (peri-)centromeric R-loops are more vulnerable to XPG or XPF in ICF cells, thus increasing centromeric breaks. This mechanism is recapitulated in DNMT3b-knockout HCT116 cells. Moreover, we present evidence for the choice of alternative end-joining (alt-EJ) repair of (peri-)centromeric breaks in ICF cells. Thus, DNA cleavages of (peri-)centromeric R-loops and mutagenic alt-EJ repair undermine centromere stability in DNMT3b defective cells. Genome-wide binding/occupancy profiling of rH2A.X by ChIP-seq in wildtype and DNMB3b-KO HCT116 cells